I worked on a (legacy now) larg-ish code base (mostly C++ '03 with some self-imposed restrictions, but extensive usage of templates) for an 'embedded' system (enterprise NAS). A full build took north of 6h on the reasonable beefy desk-side workstations available to us (we considered distributed builds, but never got to test it afair). Every once in a while there was some grumbling about the build times, but it never really improved (every three years or so we got better build machines, but by that time the code base had grown as well), partly, I suspect, due to https://xkcd.com/303/ and partly because we learned to work-around that by finding the Makefile in the tree which (likely) gave us a proper build in the shortest possible time for the files we were actually working on (not being helped by the most complex Makefile tree I've ever seen).
I very much doubt that such large build times would go over well in the Linux kernel community.
I very much doubt that such large build times would go over well in the Linux kernel community.